Total knee replacement (TKR) surgery and component systems for replacing compartments of a knee in total replacement surgery are well known. The long-term goals of TKR are to help relieve pain, improve joint function and provide a durable reconstruction with proper component and limb alignment. Typically, the surgery involves resecting the distal end of a femur so a prosthetic femoral implant component may be mounted to the femur. The prosthetic femoral implant component replaces the lateral condyle, medial condyle, and patellofemoral portions of the femur because one or more of these areas of the knee are diseased.
In TKR surgery, the proximal end of the tibia is also resected so that a prosthetic tibial implant component may be mounted to the tibia to receive the lateral and medial condyles of the femoral component. The prosthetic tibial implant component may be comprised of a material having a low coefficient of friction to simulate the meniscus being replaced by the tibial component. Commonly, the prosthetic tibial implant component is two-piece, comprising a tibial tray to be mounted to the tibia and a low-friction bearing insert to be mounted to the tibial tray and to receive the condyles of the femoral implant component.
In TKR surgery, a portion of the patella is also resected so that a prosthetic patellar implant component may be mounted to the patella. The prosthetic patellar implant component typically includes a material with a low coefficient of friction that moves along a portion of the prosthetic femoral implant component as the patient flexes and extends the leg. In some prosthetic patellar implant components, the entire implant is made of a low-friction material; in others, a low-friction bearing is mounted to a metal base.
The mechanical properties of the resected patella are inferior. The force of a retractor pushing against the resected surface can be substantial, and may lead to damage or even fracture of the thin patella. In addition, some TKR patients are older and may have substantial inferior bone quality due to osteopenia. Therefore the resected patella is also susceptible to additional damage, for example, by a saw blade. The problems associated with the inferior mechanical properties of the resected patella are avoided in TKR procedures by performing the patellar resection after the femoral and tibial resections.
However, the patella and its associated soft tissues cover substantial parts of the distal femur and proximal tibia. Accordingly, to expose the distal femur and proximal tibia, the patella is first everted laterally to expose the distal femur and proximal tibia. In everting the patella, it is turned inside out, about 180 degrees. The distal femur and proximal tibia are resected and prepared to receive the prosthetic femoral and tibial components. The patella is then resected after the femur and tibia have been resected.
Because the patella is everted, or turned inside out, during TKR, the soft tissue envelope of the knee is disrupted and the soft tissue can be placed under substantial stress. The stress on this soft tissue can disrupt the quadriceps mechanism and traumatize the extensor mechanism of the knee. This stress and trauma can lead to post-operative pain and discomfort, and the time required for patient recovery can be extensive. In addition, violation of the suprapatellar pouch can lead to heterotopic ossification and arthrofibrosis.
Accordingly, there is a need for a system and method for performing TKR surgery that achieves the long-term goals discussed above, but that also achieves the following short-term goals: minimize soft tissue trauma, minimize surgical morbidity and help speed patient recovery.